This relates in general to rotary cutting tools. One type of known rotary cutting tool is an end mill, see FIG. 1. End mills typically consist of one or more flutes including a deep helical groove that runs up the cylindrical outer surface of the milling bit. In operation, associated cutting edges may cut a work piece material; together, the flutes and cutting edges—by virtue of rotation of the milling bit—cut away and remove pieces of the work piece in a manner that creates the desired form.
One example of a known rotary cutting tool is the Z-Carb® end mill manufactured under U.S. Pat. No. 4,963,059. The U.S. Pat. No. 4,963,059 disclosed an end mill having a plurality of paired helical flutes forming an even number of helical peripheral cutting edges equally spaced circumferentially in one plane wherein the peripheral cutting edges are formed as a plurality of pairs of diametrically opposite cutting edges having the same helix angle and thereby being symmetrical with respect to the axis of the body.
End mills peripheral cutting edges remove the bulk of material, but the chip forming process starts near the corner of each edge. Repeated impact in this region can be particularly stressful to an end mill and some form of strengthening is desired.
The corners of carbide end mills can be one the weakest area of such a tool, see FIG. 2. The corners of end mills also tend to be the most vulnerable area, being most susceptible to the onset of chip damage, see FIG. 3. The increased operating parameters brought about by the ever increasing use of high performance end mill designs has furthered this concern. Several methods that have been explored and implemented to protecting these corners includes a series of grinds, which may be costly and/or difficult to control during manufacturing.
One know simple method of corner strengthening includes a chamfer. Other more complicated methods includes a corner radius, see FIGS. 4 and 5. A corner radius will reduce stresses in the areas where applied. However this method is not sufficient protection for milling most materials. Additional protection methods include a faced hook, see FIGS. 6 and 7 at FH, in which the gashing at the end of the tool is carried out to the corners. This may significantly increase the strength by making the geometry more negative, i.e. blunt; however the tradeoff is lost shearing capability and less efficient cutting.
Further methods include the above combined with various gashing methods. A blending grind may be added to the corner radius to further improve functionality and smooth the surface transition. A compromise is to blend the end gashing into the fluting to subdue the faced hook. This is commonly called a “B-Rad” (blend radius), or blend gashing. The downside is that this blend is difficult to manufacture and some of the negative geometry still exists, see FIGS. 8 and 9 at BR.
Additionally, portions of all of the above tools still tend to be subject to chipping or other generally undesired damage.